From: Milton Aupperle <milton@outcastsoft.com>

Date: December 8, 2009 9:48:56 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] cold weather..

You don't need photoshop, that's just how they do it.

You can measure the sum of pixels values in the "Photometrics" section of Astro IIDC. That's how I did it.

Basically I captured a short movie of a G2V star for each color filter, using the same exposure for all 3. Just make sure the Luma doesn't saturate, you want it at about 70 to 80%. I had bad turbulence that night, and if I hadn't I'd just have done a quick average of 10 to 20 frames.

Then I stacked each movies on that single G2V star.

Then I Imported each of the images one at a time into the Image Processing module and then do the following

After that, I clicked on the "Photom & Astrom Wind ..." (see page 62 in the manual) and then clicked on the G2V star.

In the "Photometry & Astrometry" window, the field listed as "STAR SUM:" indicates the sum of the brightness of the pixels for that star (see pages 62 & 63).

If you saved the "Photom-Astrom Log " for this file, then the field in the text file named "SumPixels".

Repeat the above for each stacked image.

Once you have the L R G B sum numbers, your basically going to calculate the ratios to the Green channel for each one.

Red Ratio = GreenSum  / RedSum

Blue Ratio = GreenSum  / BlueSum

and Green Ratio is always 1.0

I also check to see if the sum of the RGB pixel sums is close to the sum of the Luma too.

It sounds like a lot, but it it doesn't take very long. I did it watching TV after supper and did it 4 times (with LPR, without LPR, binned 1x1 and Binned 2x2) in less than an hour.

TTYL..

Milton Aupperle

On 8-Dec-09, at 8:54 PM, Mark Gaffney wrote:

Milton,

I`ve had a look at those sites & bookmarked the last one (Astropixels). I hope I remember I have it when the time is ripe. The steps involve using Photoshop which I have & seem quite specific. Some of the info on the other ones is very technical but I`ll make a note for myself of what date you sent them for future reference. (Much good this making a note does me sometimes!). I imagine it`ll be 2-3 months into next year before I can afford the Astrodon E-series filters but if I can get a grounding in B/W images in the meantime & master autoguiding to some extent I`ll be going well!

Mark.

On 09/12/2009, at 1:19 PM, Milton Aupperle wrote: